The Internet Engineering Task Force (“IETF”) Multi-protocol Label Switching (“MPLS”) working group has specified a set of standards that help provide quality of service (“QoS”) for applications running over the Internet Protocol (“IP”). The MPLS technology enables IP network operators to explicitly assign a specific path to origin-destination (“O-D”) pairs and to reserve resources along these paths. Because of this capability, MPLS allows network operators to exercise traffic engineering in the sense that if the amount of traffic between O-D pairs is known or can be estimated, then the paths between these O-D pairs (realized by the so called label switched paths (“LSP's”) and the bandwidth of the paths can be appropriately configured.
In practice, the amount of traffic that needs to be served by the network is often known only in terms of a minimum and maximum required bandwidth rather than in terms of a single bandwidth value. For instance, many (so called elastic) applications can adaptively adjust their required bandwidth to network conditions and can operate adequately if a minimum amount of bandwidth is provided. On the other hand, many applications' quality and performance does not increase after a certain level if the network provides more than a required “maximum” bandwidth.
In recent years there have been significant advances in researching and standardizing mechanisms that are capable of providing service differentiation in multi-service networks like the Internet. While there still seems to be a wide span of the methods which aim to provide QoS differentiation between contending flows, it is widely accepted that there is a need for traffic engineering mechanisms that control the access of the different traffic classes to network bandwidth resources. In particular, there is a growing interest in devising bandwidth sharing algorithms which can cope with a high bandwidth utilization and at the same time maintain some notion of fairness, such as the maximum-minimum fairness (“MMF”), proportional-rate fairness (PRF) and minimum-delay fairness.
Different aspects of the MMF policy have been discussed in various publications, mostly in Asynchronous Transfer Mode (“ATM”) Available Bit Rate (“ABR”) context, since the ATM Forum adopted the MMF criterion to allocate network bandwidth for ABR connections. However, these publications do not consider the issue of path optimization in the bounded elastic environment. Moreover, these publications do not consider the problems encompassing maximization of the minimal flow combined with optimization of the paths used by the demands. For instance, these publications study the speed of convergence of MMF allocation algorithms rather than focusing on path optimization.
In addition, MMF routing using widest-shortest, shortest-widest and shortest-distance algorithms have been studied. These algorithms do not, however, aim to explicitly maximize the carried traffic and consequently the path allocation is not formulated as an optimization task. Moreover, a number of fairness notions have been discussed and associated optimization tasks have been presented for the case of unbounded flows and fixed routes.
Although the MMF allocation has been widely accepted and studied in the literature, its appropriateness can be questioned because of the relatively low bandwidth utilization. As a result, the PRF allocation is a promising alternative to the MMF allocation. According to the PRF criterion, in the unconstrained case (i.e. when no minimum or maximum bandwidth requirement is associated with the flows), the rate allocations xd are fair, if they maximize Σd log xd under the capacity and bandwidth demand constraints. This objective may be interpreted as being to maximize the overall utility of rate allocations assuming each route has a logarithmic utility function. While the PRF allocation considers the path optimization problem, it fails to solve the problem and does not provide an efficient algorithm for path optimization when the flows are bounded.
Accordingly, there is a need for a method and apparatus for optimizing elastic flows in a multi-path network for a traffic demand.